Antenna assembly and related methods

ABSTRACT

An antenna assembly and related methods are described. The antenna assembly ( 1 ) comprises an extendible mast ( 2 ) constructed and arranged so as to be configurable between a coiled form and an extended form. The extended mast ( 2 ) is resiliently biased in the form of an elongate tube having a slit along its length. The coiled mast is wound about an axis extending transversely to the longitudinal extent of the mast. An antenna ( 6 ) is integrally coupled to the mast such that when extended, the mast supports and positions the antenna, and when coiled, the mast and antenna are coiled together.

The present invention relates to an antenna assembly, a method ofmanufacturing an antenna assembly, a method of deploying an antennaassembly and a method of stowing an antenna assembly.

Slit tubular structures, generically known as STEMs, have been usedsince the 1950's as an alternative to telescopic or jointed devices toprovide for extendable members from a small initial envelope. Theyconsist of longitudinally slit tubes, which can be opened along the slitline and coiled for compact storage or driven between the coiled andextended forms to provide a driven arm, mast or boom.

Simple slit metal tubes are mainly used in spacecraft and other areaswhere compact size was the main imperative, as they are awkward tohandle and have a very low torsional stiffness. For any applicationother than that in which a simple coil of spring metal is released for asingle-shot use, they require relatively large and heavy constrainingstructures, negating many of the advantages of the basic device.

In the 1990's, devices commonly referred to as bi-stable reeledcomposites (BRCs), as described in WO97/35706 came into general use.These manage the problems of difficult handling and complicatedmechanism by forming STEM type structures from materials that have beenengineered so as to make them easy to coil and handle, in particularmany of them exhibit a stable geometry in both the extended and coiledstates.

These bi-stable tubes have been in use as antenna supports since theearly 2000's. Large numbers are used in current theatres of operationsby the UK, US and other armed forces, as they offer the means totransport antenna masts in much smaller spaces than telescopes, jointedor articulated rods or tubes. This allows, for example, a five metremast used with the UK Armed Forces “Bowman” communications system to becarried in a rucksack side-pouch, rather than as a one point two metrelong bag of sectional glass fibre tubes that was the previous standardfor this system. Their simplicity and absence of joints also means theyare much less likely to fail in the field, where sticking joints orlocal damage to telescope sections commonly cause failure as a result ofalternating hot and cold weather conditions or relatively minor impactincidents.

Whilst these masts provide for more reliable and far more compact meansof elevating an antenna to improve performance, the antennas themselvesare largely those in use on the previous generation of masts and can becumbersome, sometimes taking up significantly more space in carriage andweighing more than the new generation BRC mast used to support them.

According to a first aspect of the present invention, there is provided

-   -   an antenna assembly, comprising:    -   an extendible mast constructed and arranged so as to be        configurable between a coiled form and an extended form, wherein        when extended the mast is resiliently biased in the form of an        elongate tube having a slit along its length and wherein when        coiled the mast is wound about an axis extending transversely to        the longitudinal extent of the mast; and,    -   an antenna integrally coupled to the mast such that when        extended, the mast supports and positions the antenna, and when        coiled, the mast and antenna are coiled together.

Thus, the antenna assembly provides an extendible mast with an integralantenna which advantageously allows the antenna and the mast to becoiled and extended together, greatly simplifying the deployment,storage and transportation of such devices. The antenna assembly can bestored and transported in its coiled form, and then deployed by simplyextending the mast such that the antenna is positioned forreceiving/transmitting signals. In prior art schemes for deployingantennas in the field, the antenna would be a standard antenna, notdesigned for use with any particular mast, which would be transportedseparately from the mast and then fixed to the distal end the mast atthe point where the mast is to be erected. Such prior art schemes areclearly cumbersome and problematic compared with the present invention.

The antenna assembly can in principle be operated with a wide variety ofantenna types and different sizes of mast according to need. The mast ispreferably made from a relatively thin material or materials to aidcoiling, e.g. between 1 mm and 5 mm. The antenna element or elementscomprising the antenna are preferably also thin, e.g. no more than 2 mm,so as not to significantly affect the ability of the mast to coil. Thus,the antenna can be entirely contained within the footprint of the mastwithout significantly adding bulk to the overall assembly.

In embodiments, the antenna is formed from one or more antenna elements.The or each antenna element may have a significant extent in thelongitudinal direction of the mast, e.g. greater than 5 cm, or greaterthan 20 cm, or greater than 50 cm in some instances.

In some embodiments, the antenna can extend substantially all of theextent of the mast. In other embodiments, the antenna is distanced fromthe bottom of the mast, by for example at least a quarter, or a half, orthree quarters of the longitudinal extend of the mast, so as to beelevated when the antenna assembly is erected.

The mast can progressively extend from being coiled to its slit tubeform. Thus, in embodiments, the mast can be completely or partiallyextended when deployed, as desired.

In an embodiment, the antenna is not provided by any structuralcomponent of the mast, e.g. material that completely or significantlyprovides the axial stiffness or bending stiffness needed to keep themast erected, or the hoop modulus needed to provide the resiliency whenin the slit tube form, and generally resist the stresses and strainsacting on the mast when deployed and supporting the antenna. Thus, theantenna is not constrained to extending the entire length of the mast.The antenna and the mast may also be formed from different materials.

In an embodiment, the antenna is bonded to a surface of the mast. Anysuitable adhesive or bonding technique can be used according to thematerials used for the antenna and mast.

In an embodiment, the antenna is bonded within a structural component ofthe mast. Thus, the antenna is integrated within the mast within thematerial of the mast which is contributing to the structural propertiesof the mast.

In an embodiment, a structural component of the mast comprises aconductive material, the assembly comprising an insulating layerdisposed between the conductive element and the antenna. This allowsconductive materials to be used without affecting the antenna inoperation.

In an embodiment, the antenna comprises a woven material, braid orperforated material to accommodate strains induced in the antenna whenthe mast is coiled. In embodiments where the antenna is bonded to thesurface or near the surface of the mast, the use of these materials forthe antenna helps avoid delamination or damage to the assembly due tothe strains involved in coiling and extending the mast.

In an embodiment, the antenna is positioned at the neutral axis ofbending of the mast. This provides another technique for bonding theantenna to the mast to help avoid delamination or damage to the assemblydue to the strains involved in coiling and extending the mast.

In an embodiment, the mast comprises a pocket that receives the antennasuch that the antenna can slip relative to the mast. In order words, theantenna is loosely attached to the mast so that there can be relativemovement between the two to accommodate strains when the mast is coiledand extended. The pocket may for example be formed by the mastcomprising a sheet or sheets of material on the front or rear surface ofthe rest of the mast attached at different circumferential positions soas to form a space behind it, i.e. the pocket. The sheet or sheets maymake no significant contribution to the structural requirements of themast. Thus, the sheets can be thin which helps avoid any conflict withthe rest of the mast being able to coil and extend.

In an embodiment, the mast comprises a reinforced composite. Thus, themast can be made from layers of fibre reinforced polymer or the like. Inan embodiment, the mast comprises a bistable material. It is anticipatedthat these materials will be preferred materials for forming the mast inmany applications.

In an embodiment, a structural component of the mast comprises aconductive material, wherein the component also serves as the antenna.For example, the mast may be made from a fibre reinforced compositestructure, wherein a layer of composite reinforcement is conductive. Forexample, one or more layers can be formed from glass fibres and one ormore other layers can be formed of carbon fibre, which is conductive andwhich can serve as the antenna.

In an embodiment, the antenna assembly comprises a connector on the mastfor connecting the antenna assembly to a communications system. Wherethe antenna is entirely enclosed within the material of the mast, a holein the mast or wires protruding through the mast may be provided toaccess and connect to the antenna.

In an embodiment, the connector is positioned on the mast at a distancefrom the antenna, the assembly comprising a cable integrally coupled tothe mast along a portion of the mast to connect the antenna andconnector, the mast and cable are coiled together.

In an embodiment, the antenna assembly comprises a pocket at a side edgeof the mast in which the cable is retained. Due to the slit tube form ofthe mast, two side edges are formed running the longitudinal extend ofthe mast, either or both of which can be provided with a pocket formedin the material of the mast or from additional material bonded or fixedto the mast. In the coiled configuration, the mast is flattened out atthe slit in the tube so that the side edges are at the sides of thecoil. Thus, the cable in the pocket is coiled with the mast at the sidesof the coil such that it lies outside the footprint of the mast, i.e. itis not in the interstitial spaces of the coiled mast, meaning that thecoiling of the cable does not interfere with the coiling of the mast.

In an embodiment, the antenna assembly comprises a housing forcontaining the coiled mast and guiding the mast as it is extended. Thehousing may have has a winding mechanism for coiling or extending themast, or both. Thus, the antenna assembly may be extended and retractedmanually, allowed to self extend by the release of a mechanismconstraining the coiled assembly, extended from containers designed tohold the coiled device or mechanised to allow deployment by handcranking or by means of a powered system. Use may be made of any of theabove means in providing specific embodiments of the current invention.

According to a second aspect of the present invention, there is provided

-   -   a method of manufacturing an antenna assembly, comprising:    -   integrally coupling an antenna to an extendible mast, the mast        being constructed and arranged so as to be configurable between        a coiled form and an extended form, wherein when extended the        mast is resiliently biased in the form of an elongate tube        having a slit along its length and wherein when coiled the mast        is wound about an axis extending transversely to the        longitudinal extent of the mast, such that when extended, the        mast supports and positions the antenna, and when coiled, the        mast and antenna are coiled together.

According to a third aspect of the present invention, there is provided

-   -   a method of deploying an antenna assembly, the antenna assembly        comprising:    -   an extendible mast constructed and arranged so as to be        configurable between a coiled form and an extended form, wherein        when extended the mast is resiliently biased in the form of an        elongate tube having a slit along its length and wherein when        coiled the mast is wound about an axis extending transversely to        the longitudinal extent of the mast, and, an antenna integrally        coupled to the mast such that when extended, the mast supports        and positions the antenna, and when coiled, the mast and antenna        are coiled together,    -   the method comprising positioning and extending the mast from        the coiled form to the extended form so as to elevate the        antenna.

According to a fourth aspect of the present invention, there is providedan antenna assembly comprising:

-   -   an extendible mast constructed and arranged so as to be        configurable between a coiled form and an extended form, wherein        when extended the mast is resiliently biased in the form of an        elongate tube having a slit along its length and wherein when        coiled the mast is wound about an axis extending transversely to        the longitudinal extent of the mast; and, an antenna integrally        coupled to the mast such that when extended, the mast supports        and positions the antenna, and when coiled, the mast and antenna        are coiled together,    -   the method comprising coiling the mast from the extended form.

In embodiments, any of the methods described above is used with anantenna assembly according to any example or embodiment describedherein.

It will be appreciated that any features expressed herein as beingprovided “in one example” or as being “preferable” or an embodiment maybe provided in combination with any one or more other such featurestogether with any one or more of the aspects of the present invention.

Embodiments of the present invention will now be described by way ofexample with reference to the accompanying drawings, in which:

FIG. 1 shows a perspective view of an example of an antenna assemblyaccording to an embodiment of the present invention;

FIG. 2 shows a perspective view of an example of an extendible mastsuitable for use with the antenna assembly of FIG. 1.

FIG. 3 shows in cross section an example of an antenna assembly;

FIG. 4 shows in cross section another example of an antenna assembly;

FIG. 5 shows in cross section yet another example of an antennaassembly;

FIG. 6 shows a perspective view of an example of an antenna assembly inthe extended configuration;

FIG. 7 shows a perspective view of the antenna assembly of FIG. 6 in thecoiled configuration;

FIG. 8 shows in cross section still another example of an antennaassembly;

FIG. 9 shows in cross section a housing for dispensing an antennaassembly; and,

FIG. 10 shows in cross section another housing for dispensing an antennaassembly.

FIG. 1 shows an example of an antenna assembly 1. The assembly 1comprises an extendible mast 2 incorporating an integral antenna 6formed from one or more antenna elements along some or all of its length(shown in broken line in the example of FIG. 1). References made hereinto the longitudinal or axial direction of the mast 2 or antenna assemblygenerally refer to the direction in which the mast is extended. The mast6 has a top cap 3 and a bottom cap 4 which attach to the ends of themast. Optionally, tethers 5 are attached the top of the mast or to thetop cap 3 and are pinned to the ground to help anchor the antennaassembly 1 in place. Alternatively, the assembly 1 can be selfsupporting.

The antenna assembly 1 has a connector 7 by which connection can be madeat a convenient point to the antenna assembly 1 by a cable 8, e.g. aco-axial cable, for connecting the antenna assembly 1 to a communicationsystem 9. Where the connector 7 is at some distance from the antenna 6,the mast may include a cable 18 to connect the two.

The extendible mast 2 has the form of a STEM (slit tubular extendiblemember). Thus, as shown in more detail in FIG. 2, the mast 2 is formedof an elongate member of sheet-like material, i.e. the member is thin incross section, e.g. typically between 1 mm and 5 mm. The member can beopened out into a flat form allowing it to be wound into a coil 11. Theextended portion 12 is resiliently biased to have a cross section thatis curved, in this example, in the form of a circle or partial circle.Thus when fully extended, the member is resiliently biased in the formof a slit tube. The sides of the tube may meet or overlap to form a fulltube, or a gap may be left. Cross sections other than circular may beused. For example, ovals and other continuous, non-circular arcs for thecross section can also be produced. The cross section may have straightportions between curved portions whilst being generally curved. Theantenna is integral with the extendible mast so as to be able to coiland uncoil with the mast 2. Various techniques for doing this aredescribed in the following disclosure.

Thus, with the end cap 3 and bottom cap 4 removed, the antenna assembly1 can be progressively wound/unwound around an axis perpendicular to itslongitudinal extent between a fully coiled form and a fully extendedform. If desired, a housing can be provided to contain the coiledantenna assembly and to help guide the extension of the mast.

The techniques described herein allow the production of STEM type masts2 that integrate the antenna function with that of the coil-able mast 2,reducing pack size and often weight and greatly simplifying thedeployment of communications antennas. Whilst the techniques could allowthe production of integral mast and antenna systems using any mast 2that falls into the general category of a STEM, provided the materialbase used for the mast 2 is not such as to interfere with the RFrequirements of the antenna 6, it is anticipated that implementationwill in many cases use composites, Fibre Reinforced Plastics (orPolymers) (FRPs) or Bistable Reelable Composite type devices, as theircharacteristics are well suited to this type of use. Other material,such as polymers with good elastic properties or metals may be used butin general FRP produce a product of superior performance.

FRPs are known per se and are not described in detail herein. However,in brief, FRPs are composite materials made of a polymer matrixreinforced with fibres. The fibres are usually fiberglass, carbon, oraramid, while the polymer is usually an epoxy, vinylester or polyesterthermosetting plastic or thermoplastic, such as polypropylene,polyethylene nylon or poly-ether-ether-ketone. Although the use ofthermosetting resins has formed the traditional basis for FRPmanufacture, thermoplastic matrix polymers are increasingly being used,due to their speed of production and often superior mechanicalperformance. The use of fibrous materials mechanically enhances thestrength and elasticity of the plastics. The original plastic materialwithout fibre reinforcement is known as the matrix. The matrix is atough but relatively weak plastic that is reinforced by stronger stifferreinforcing filaments or fibres. The extent that strength and elasticityare enhanced in a fibre reinforced plastic depends on the mechanicalproperties of both the fibre and the matrix, their volume relative toone another, and the fibre length and orientation within the matrix.Often FRPs are manufactured by consolidating or laminating differentlayers of material together. As described below, this layering techniquecan be used to integrally couple the antenna to the mast by placing theantenna within the laminate.

In one example, the material used for the mast 2 is a BRC comprisingbistable member, whether made of FRP or otherwise. Such a bistablemember has a first stable state in the coiled form, wherein the crosssection of the member is generally flat and a second stable state in theextended form, wherein the cross section of the member is curved aspreviously described. Preferably, the bistable member is capable ofreversible configuration between its coiled and extended forms aplurality of times. Suitable structures are disclosed in the followinginternational patent applications, each of which is incorporated here byreference. WO-A-88/08620, WO-A-97/35706, WO-A-99/62811, andWO-A-99/62812. Such bistable structures are available from RolaTubeTechnology Limited of Lymington, United Kingdom.

As described in the above-referenced patent applications, such abistable member generally comprises material that creates a bias towardsconfiguring the material in the extended form (e.g. having a circularcross-section in this example), as well as material that creates a biasopposite to the first bias (e.g. one that biases the member towards itsflattened, retracted or coiled form). The member can comprise aresilient substrate, made of metal for example, which is biased towardthe extended form (e.g. biased toward making the member have a circularcross-section), laminated with a plastic layer that tends to bias themember towards the retracted form (e.g. having a flattenedcross-section). Alternatively, the member can comprise a strip or sheetof a thermoplastic material having prestressing means attached theretoor embedded therein. One particular example is a thermoplastic striphaving prestressed fibres therein (such as fibres of glass, carbon orpolymeric materials). The fibres can be located at different anglesrelative to each other in the plane of the coiled member, such ascomprising one set of fibres that are longitudinally extending and asecond set of fibres that are transversely extending Suchfibres-reinforced composite members (e.g. a thermoplastic resin, such aspolyethylene or polypropylene, with fibres of another material, such asglass, carbon, or aramid, embedded therein) are preferred for use in thepresent invention.

It is clear that a mast 2 made from a simple metal or otherwiseconductive STEM could itself, in fact, be used as a form of antenna aswell as contributing to the required structural characteristics of themast. This does not, however, lend itself to use in most moderncommunications systems. This is primarily because of the need to tailorthe length of the antenna 6 independently of the height to which it isdesirable to raise the functional antenna. The division into sections ofmost high gain antennas, the use of balancing electronic circuits thatneed to be placed close to junctions in antenna elements and the otherrequirements of efficient RF design all mean this simple approach is ofuse only in a small number of circumstances. A high frequency, the 2 to4 GHz bands of modern cellular communications for example, antenna mayonly be a few centimetres across but good reception may require this tobe several metres in the air.

Thus, in most cases it is expected that the mast 2 and antenna 6 willcomprise respectively dissimilar material. In order to combine thefunctions of antenna 6 and mast 2 in a single assembly 1 it is clearfrom the discussion above that the dissimilar materials will need to becombined in such a manner that the antenna 6 is not adversely affectedby the repeated coiling and uncoiling of the STEM mast 2.

If the antenna 6 is small, for example the 2 to 4 GHz type describedabove, this can be achieved by either bonding a simple conductive foilantenna to the mast 2 (as shown by FIG. 3), or by embedding theconductive element within the lamina of a composite (e.g. FRC or BRC)mast (as shown by FIG. 4).

If the antenna element 6 is fully embedded, then provision either of aconductive wire or other element that runs through to the surface toallow connection, or of a hole or cavity 14 (as shown in FIG. 4) in thestructure of the STEM 2 must be made to allow connection of the antenna6 to the external communications apparatus 9.

If the material of the STEM is conductive, an insulating layer 15 mustbe placed to act as a barrier between the STEM 2 and the antenna element6 or elements, as shown in FIG. 5.

In the case of longer antenna elements, the same general techniques asshown in FIGS. 3 to 5 can be used, with now the additional issue ofincorporating the antenna 2 to the mast 2 in such a manner as to preventthe action of coiling the antenna assembly 1 causing it to be damaged.This can be achieved for example in the ways summarised as follows:

-   -   By attaching the antenna 6 in such a manner as to allow it to        slip relative to the material of the mast 2, thus isolating it        from the strains occurring at the surface of the mast 2 during        coiling and extension    -   By forming the antenna 6 from a material that is capable of        tolerating repeated cycles of extension and retraction    -   By positioning the antenna 6 on or close to the neutral axis of        bending of the mast 2, such that the strain it experiences when        coiled and extended is minimal

In the case of an antenna 6 that is loosely coupled, allowing sliprelative to the STEM mast 2, any material that is suitable from anelectrical point of view may be used to form the antenna 6 provided itsnature is such that it does not interfere with the coiling of the STEMmast 2. In practice this means that it will usually be formed of a thinmaterial, metallic films, metal coated polymer films, woven or braidedwire cloths or other conductive polymer or fabric materials are amongstthe materials that could be used successfully. Whilst there will in mostcases be a requirement for some thicker elements in the form of ferritechokes and balun transformers, or some electronic circuits that need tobe sited close to the antenna feed point, these need to be localised,such as to form a small, local discontinuity in the coiled profile ofthe STEM, such as not to interfere with its coiling. Where an electricalrequirement may exist for a component with a physical size and shapesuch that it cannot be rolled interstitially with the STEM, the optionexists to site it on the edge of the STEM.

FIG. 6 shows an example where the inner surface of the STEM 2 has aplurality of “slats” 20 a, 20 b, 20 c . . . at intervals along itslength. Each slat 20 a,20 b,20 c is attached at its ends to at twopoints across the STEM 2 such that a pocket is formed behind the slats20 a, 20 b, 20 c. Some of the slats, such as slat 20 c, are shown inFIG. 6 in a position where they are raised from the inner face of theSTEM 2 to illustrate this. The antenna 6 can be positioned within thispocket created by the slats 20. To ensure the antenna 6 does not slipcumulatively over cycles of extension and retraction, one end of theantenna 6 can be secured to the mast 2. It may be desirable to attachthe other end to the mast 2 with an extensible elastic coupling in orderto prevent buckling of the antenna 6 and ensure smooth extension andretraction. In this way the antenna 6 will be held under tension againstthe fixed attachment of the other end. Thus, the antenna 6 can beintegrally included with the mast 2 in such a way that the mast 2 can becoiled (as shown in FIG. 7) with the antenna 6 in the interstitialspaces between the coils and extended (as shown in FIG. 6).

From a production and use point of view, the technique of allowing slipbetween the antenna 6 and the structure of the mast 2 creates someadditional challenges. Separating the antenna 6 mechanically from thebody of the STEM, although it is possible to provide some sort of loosecover within which it is protected from the external environment butmade as, for example, a covering layer on the STEM that has an un-bondedarea to act as a pocket within which the antenna sits, can lead to adevice with more potential points of failure and the sliding action hasthe potential to cause wear on both the antenna and the STEM. For thisreason, other techniques where the antenna 6 is bonded to the mast 2, asdescribed below, may be preferred in some implementations.

If the antenna element or elements 6 are to be bonded to the surface ofthe STEM or to a part of the STEM that is at a significant distance fromthe neutral axis, then the choice of material needs to be such that theextension and coiling of the STEM will not degrade its performance. Inpractice this means using a material that is highly extensible along theprinciple axes of the STEM. Simple metal foils or metallised polymerfilms tend to perform poorly in this context. Not only is the bonding ofthem to most, fibre reinforced polymer based STEM structures in currentuse in this context difficult but they respond poorly to cyclic strain.The simplest solution to this problem is to use antenna elements formedfrom woven or braided conductive fabrics, in which the fibre angle liesat a significant angle relative to the principle axis of the STEM. Thisfunctions to provide a viable practical solution in two ways:

-   -   The open texture of the material allows the polymer base of the        STEM, either during production of during a post fixing        operation, to be continuous through the open weave or braid.        This ensures good mechanical fixing, even if the adhesion of the        materials is not sufficiently good for a straightforward        adhesive bond to take the repeated cyclic strains of operation.    -   The woven or braided structure exhibits a very high Poisson's        ratio. Thus when the STEM is coiled, the extension along the        axis causes the fibres to move relative to each other in the        manner of a lattice fence, the extension along the long axis        causing shortening along the hoop axis in sympathy with the        surface strains of the STEM as it is coiled. On extension, this        is reversed. The effect is to reduce the strain on the        individual conductive fibres to a very low level.        Characteristically in a BRC type STEM the axial surface strains        will be of the order of 2%. The fibre strains in a fabric with        angles of 45 degrees to the axis in its weave will be reduced to        between about 0.15% to 0.3%, a level comfortably within the        tolerance for cyclic strain of most conductive materials. This        can be manipulated by varying the fibre angle allowing some        compensation for variations in the mast structure and the        characteristics of the antenna material. In practice most        bi-stable structures are made with fibre angles in the surface        layers lying between plus and minus 30 degrees to the long axis        of the structure, this will also tend to be the case for woven        or braided antenna elements.

This Poisson ratio effect in surface layers is exploited in BRC typeSTEMs to produce their fundamental characteristics of an engineeredlevel of bi-stability and coherent extension and coiling. If used on aBRC STEM, the conductive fabric is therefore operating in sympathy withthe underlying structure and therefore the shear strains of the antennarelative to the underlying STEM are reduced to close to zero, furtherimproving the bond integrity and minimising the likelihood of failure inoperation.

If the antenna elements 6 are to be fully embedded within the structureof the material of the underlying STEM as a discrete layer or lamina,then provided they are located close to the neutral axis of bending ofthe STEM the cyclic strain is greatly reduced and the antenna materialcan be chosen without particular concern as to this aspect of itsperformance. Any material, when bent, will experience extension on theextrados face and compression on the intrados face. It therefore followsthat at some point within the material plane a level will experienceneither extension nor compression, this is known as the neutral axis ofbending. For a homogeneous, orthotropic material the neutral axis willlie at or close to the central plane of the material normal to the majorand minor axes of bending. Although for non-orthotropic materials, suchas laminar composites, the location of this point of zero axial strainmay translate slightly from the central plane during bending, locating amaterial that is relatively inextensible at this point within thematerial of the mast will minimise the strains experienced by it duringbending.

The bonding of the antenna material to that of the STEM mast 2 does,however, become critical when included within the structure of the STEMmast 2.

If the antenna elements 6 are to be placed as discreet layers formingpart of what, regardless of the nature of the STEM will, by definitionbecome a laminar structure consisting of insulating structural elementseither side of the conductive antenna. This means the bonding of thelamina has to be such as to reduce any potential impact of local shearforces to the point where de-bonding does not occur

This can be addressed by:

-   -   Using a woven or braided or perforated conductive material for        the antenna 6, in much the same manner as described above, with        the exception that the angles of the fibres in the weave or        braid are no longer critical to the cyclic strain placed on the        conductive fibres. Where a perforated material is used, it may        be advantageous for the perforations to be arranged in such a        manner that the continuous lines that can be drawn between        perforations lie along angles other than the major and minor        axes of bending thus reducing the continuous strain applied to        the material.    -   Using a material for the antenna 6 that is compatible with the        material of the STEM 2, such that a good enough adhesive bond is        obtained during manufacture—certain epoxy resins, for example,        may produce a good enough bond to a metal that a STEM formed        from an epoxy matrix composite can tolerate the inclusion of a        metal or other conductive layer within its structure    -   Forming the antenna 6 as an integral part of the fibre        reinforcement of a fibre reinforced composite structure. The        technology exists to form a layer of composite reinforcement        such that parts of its area may, for example, be formed from        glass and others of carbon fibre, which is conductive. In this        manner a pre-formed sheet of reinforcing material could be        manufactured that has the pattern of the antenna present within        it as a change in the nature of the fibre reinforcement in some        areas of its structure. This can then be processed to form a        composite STEM in any of the ways known to a practitioner of the        art.

In most cases, the antenna 8 will terminate electrically some distancefrom either end of the supporting STEM mast 2. Although electricalconnection can be made to a separate cable 8 at the feed point of theantenna 6, it is clearly desirable to be able to make this connection atsome point convenient to the user. To this end, a cable may be embodiedin the STEM mast 2 to connect the antenna 2 to the connector 7.

FIG. 8 shows one way of accomplishing this by running the cable 18within a pocket 16 along the edge of the STEM mast 2. This isparticularly well suited to use with co-axial cables or others thatrequire a significant diameter in order to function. By positioning thecable 2 at the edge, any increase in the overall thickness of thestructure can be eliminated or kept to a minimum, so its affect on theability of the mast 2 to coil is minimised. In contrast, if the cablewas positioned on the face of the mast, the whole structure will distortduring coiling as one part of it is separated by the additional cablegap and other parts are not. It would then be necessary to increase thethickness of the STEM elsewhere to compensate, leading to a large,unmanageable coil.

Alternatively, connection to the antenna 6 can be accomplished by one ormore thin conductive elements bonded to the surface of the STEM mast 2running along its length. Alternatively, connection to the antenna 6 canbe accomplished by one or more thin conductive elements can be embeddedwithin the material of the STEM mast 2 running along its length.

In practice the choice will be related to the nature of the antennaelement 6. If this requires a co-axial feed, then it will usually provepreferable to run a co-axial cable 18 in a pocket 16 along the longedge, as shown in FIG. 8. If there is no need for a co-axial feed, thenif the antenna element 6 is bonded to the surface of the STEM mast 2, itmay prove more straightforward to bond the conductors to the surface.Similarly, if the antenna 6 is embedded within the structure of the STEMmast 2, it may prove more straightforward to also embed the conductiveelements leading to the connection point 7 within the structure of theSTEM mast 2.

The techniques described herein allow the production of STEM type masts2 that integrate the antenna function with that of the coil-able mast 2,reducing pack size and often weight and greatly simplifying thedeployment of communications antennas. As illustration, an example of anantenna assembly made according to the principles disclosed herein has amast that is 5 meters high having a 7.5 cm diameter, with an elevateddipole antenna element the bottom of which is located 2.5 m from thebottom of the mast. This antenna assembly 1 is capable of coiling into acylindrical space 18 cm in diameter and 25 cm high, and weighs about 4kg.

The assembly 1 may be provided with a housing 50 which contains thecoiled mast 2 from which it can be extended wholly or partially. Thehousing 50 may form a base for supporting the extended antenna assemblywhen deployed. FIG. 8 shows a housing 50 that provides a simple“push-pull” cassette, which holds the coil 11 in place and allows themast 2 to be push-pull extended and retracted. The housing 50 mayinclude a releasable mechanism that constrains the coiled portion 11 ofthe mast 2, such that releasing the mechanism allows the mast 2 to selfcoil. The housing 50 may include a hand-operated or motor drivenmechanism for winding/extending the mast 2 that is arranged such as todrive the mast 2 between extended 12 and coiled 11 states. For example,FIG. 9 shows a housing 50 comprising a pinch-wheel 51 operable to drivethe mast 2.

As will be appreciated many other means are available to provide thehousing 50 and drive to the mast 2. The housing 50 may provide completecontainment or be composed of rods or rollers arranged around the coil11, closely enough spaced to prevent it going in between the rods orrollers when in use, but thus reducing friction on the surface of thecoil.

Embodiments of the present invention have been described with particularreference to the example illustrated. However, it will be appreciatedthat variations and modifications may be made to the examples describedwithin the scope of the present invention.

1-21. (canceled)
 22. An antenna assembly, comprising: an extendible mastconstructed and arranged so as to be configurable between a coiled formand an extended form, wherein when extended the mast is resilientlybiased in a form of an elongate tube having a slit along its length andwherein when coiled the mast is wound about an axis extendingtransversely to a longitudinal extent of the mast; and, an antennacoupled to the mast such that when extended, the mast supports andpositions the antenna, and when coiled, the mast and antenna are coiledtogether.
 23. The antenna assembly according to claim 22, wherein theantenna comprises a woven material, braid, or perforated materialcoupled to the mast.
 24. The antenna assembly according to claim 23,wherein the antenna extends part way along the mast having a first endoffset from a base of the mast and/or a second end offset from a top ofthe mast.
 25. The antenna assembly according to claim 23, wherein thewoven material or braid comprise fibres that are angled relative to thelongitudinal extent of the mast or the perforated material hasperforations arranged such that continuous lines are present betweenperforations and those lines are angled relative to the longitudinalextent of the mast.
 26. The antenna assembly according to claim 22,wherein the antenna is positioned at a neutral axis of bending of themast.
 27. The antenna assembly according to claim 22, wherein the mastcomprises a reinforced composite and/or a bistable material.
 28. Theantenna assembly according to claim 22, the assembly comprising a cablecoupled to the mast along at least a portion of the mast such that themast and cable are coiled together, the cable being electricallyconnected to the antenna.
 29. The antenna assembly according to claim22, comprising a connector on the mast for connecting the antennaassembly to a communications system.
 30. The antenna assembly accordingto claim 29, wherein the connector is positioned on the mast at adistance from the antenna, the cable arranged to connect the antenna andconnector.
 31. The antenna assembly according to claim 22, comprising apocket in which the cable is retained.
 32. The antenna assemblyaccording to claim 31, wherein the mast has first and secondlongitudinal side edges, the assembly comprising a pocket at one or bothside edges of the mast in which the cable is retained or in whichrespective cables are retained.
 33. The antenna assembly according toclaim 31, wherein the cable runs along a portion of the mast that isless thick than other portions of the mast.
 34. The antenna assemblyaccording to claim 31, wherein the cable lies outside the interstitialspaces of the coiled mast.
 35. The antenna assembly according to claim31, wherein the mast comprises structural layers of material and thepocket is formed between the layers of material of the mast or thepocket is formed from additional material bonded or fixed to the mast.36. The antenna assembly according to claim 31, wherein the cable iscoaxial.
 37. The antenna assembly according to claim 31, wherein thecable comprises conductive elements bonded to the surface of the mast orembedded within the material of the mast running along its length. 38.The antenna assembly according to claim 31, wherein either: i) the mastcomprises structural layers of material with the antenna located betweenlayers of the material, and wherein the cable also runs between thoselayers of the material, or ii) the antenna and the cable are bothlocated at the surface of the mast.
 39. The antenna assembly accordingto claim 31, wherein the antenna has a feed point, the assemblycomprising an electronic circuit or components connected to the cableand the antenna feed point, wherein the electronic circuit or componentsare localized close to the antenna feed point, such as to form a small,local discontinuity in the coiled profile of the STEM, such as not tointerfere with its coiling.
 40. A method of manufacturing an antennaassembly, comprising: coupling an antenna to an extendible mast, themast being constructed and arranged so as to be configurable between acoiled form and an extended form, wherein when extended the mast isresiliently biased in the form of an elongate tube having a slit alongits length and wherein when coiled the mast is wound about an axisextending transversely to the longitudinal extent of the mast, such thatwhen extended, the mast supports and positions the antenna, and whencoiled, the mast and antenna are coiled together.
 41. The method ofclaim 40, comprising coupling a cable to the mast along at least aportion of the mast such that the mast and cable are coiled together,the cable being electrically connected to the antenna.